‘Dinosaurs Among Us’ Retraces an Evolutionary Path

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Archaeopteryx was described in the 1860s by Thomas Henry Huxley from its fossil specimen as having feathers but many reptilian features.CreditCreditZhao Chuang/Peking Natural Science Organization, via American Museum of Natural History

At a preview of the new American Museum of Natural History exhibition “Dinosaurs Among Us,” scientists gave a tip of the hat to Thomas Henry Huxley, the man who proposed in the 1860s that dinosaurs never really vanished from Earth. Most did go extinct, but their evolutionary legacy lives all around us. They are birds, all 18,000 species of them.

While Charles Darwin’s book of books, “On the Origin of Species by Means of Natural Selection,” was still in print in 1859, Huxley, a lecturer in paleontology and natural history in London, wrote a favorable review and became a convert to Darwin’s theory. In a debate the next year, Huxley got the better of the bishop of Oxford, and became known thereafter as Darwin’s bulldog. He was also the first in a long line of Huxleys who distinguished themselves in science and the arts.

A few years later, Huxley enlisted Archaeopteryx, a fossil specimen found in a Bavarian limestone quarry, in his defense of Darwin. He was struck by the specimen’s many reptilian features; but for a feather in the fossil, it would probably have been misidentified as a reptile. In a report in 1867, Huxley established the evolutionary relationship of birds and reptiles, citing 14 anatomical features that occur in birds and reptiles alike, but not in mammals.

Archaeopteryx was one of those “missing links” in the fossil record that Darwin worried was a weakness in this theory of evolution. Huxley called attention to the feathers and wishbone of this early bird and the long bony tail of a reptile. This was a species in transition.

Why has it taken so long to recognize that Huxley had almost certainly been right about the origin of birds from some meat-eating theropod dinosaurs?

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Archaeopteryx and fossils like those of Khaan mckennai have helped establish the evolutionary relationship between birds and reptiles.CreditM. Ellison/American Museum of Natural History

Mark A. Norell, the chairman of the division of paleontology at A.M.N.H. and curator of the exhibition, had long been a staunch proponent of a dinosaur-bird link. A lot of evidence amassed over the last two decades, especially the numbers of feathered dinosaurs found in China, moved paleontologists to organize the exhibition as a kind of victory lap.

“I think this is really going to shake up the way people think of dinosaurs,” Dr. Norell said.

Most ornithologists, though not completely won over, had already ceased raising blanket objections to the dinosaur-bird link. They seemed at a loss to conceive of alternative explanations for the gathering evidence, paleontologists say.

The slow evolution of the practice of paleontology itself was another reason for the delay in recognizing Huxley’s insight. For the rest of the 19th century and the first half of the 20th, the big game of fossil hunting was the bigger and more bizarre dinosaurs that drew people to museums. Expeditions to remote lands widened the search to nearly all continents, piling up skeletons faster than could be analyzed in depth.

Roy Chapman Andrews became the real-life Indiana Jones in the 1920s, bringing back from the Gobi Desert of Mongolia a variety of new dinosaur species and the first dinosaur eggs. If only he had found feathered dinosaurs then and there, paleontologists say, the dinosaur-bird link might have been recognized much sooner. That was not to happen until the end of the century.

By that time, the field work of fossil hunters remained important, but only as the first step in discovery. For example, in 1964, John H. Ostrom of Yale University saw a birdlike claw sticking out of the ground in Montana. He named the dinosaur Deinonychus, or “terrible claw.” But it reminded him of Huxley’s evolutionary insight, leading Dr. Ostrom to link birds to new generations of dinosaur research.

In the last two or three decades, biological disciplines have joined dinosaur studies, applying tools capable of transcending the terrible claw limitations of fossilized skulls and bones. Geologists once dominated the field, Dr. Norell said, but “now so many of us could be called paleobiologists.”

Also, thousands of fossils with feather imprints have been discovered in Liaoning Province in northeastern China in the last 15 years, Dr. Norell said. Birds are the only feathered creatures alive today, but 150 million years ago, early birds and dinosaurs of all shapes and sizes came with feathers, not necessarily for flight. Feathers, museum researchers said, are one of the most useful skin coverings that ever evolved for insulation or mating display as well as gliding or powered flight.

Paul C. Sereno, a University of Chicago paleontologist, has analyzed many recent Chinese fossils of animals that had lived more than 100 million years ago that were found in lake bed sediments.

“Huxley was a brilliant anatomist,” Dr. Sereno said. “Some of the first birds from the Chinese site look just like Archaeopteryx. This time, the dinosaur-bird transition has become ascendant.”

So what is there not to like about evolution if it indeed accounts for the few surviving dinosaurs transformed into flocks of birds? Monstrous dinosaurs may captivate first graders, who thrill at being scared at a safe distance in time.

They may also draw comfort from knowing the eating habits (carnivore or herbivore) of dinosaurs — their know-it-all grown-ups can’t even pronounce their names. Need there be more reason for a fascination with strange and mighty dinosaurs when you are little in a big world?

From my back porch in the country, I hear crows squawking high in the trees. Crows are smart, clever enough to pry open garbage cans down the road, if raccoons had not gotten there first — which might account for their squawking. Some birds, like blue jays at the feeder, seem to enjoy chasing off chickadees and sparrows.

Better to be hearing the bullying jays or cardinals singing their vespers, however, than to have a fearsome T-rex peering in at you through your upstairs windows at daybreak, ready for breakfast.